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A Variational Assimilation Technique In A Hybrid Isentropic-sigma Coordinate

Abstract

A three-dimensional variational (3dVAR) analysis set in a generalized vertical coordinate is described. This analysis technique has been applied to the Rapid Update Cycle (RUC), a mesoscale analysis/model system in the United States providing high-frequency, short-range forecasts. The RUC 3dVAR analysis is, in fact, set in a hybrid isentropic-sigma coordinate, but without loss of generality or applicability to other coordinate systems. The use of this coordinate provides an adaptive analysis space, with sloping of background error covariances in the proximity of baroclinic systems, and a stability-dependence for vertical error covariances. The basic characteristics of the RUC are described briefly, with special attention to its vertical coordinate. A detailed description of observation operators is provided. The WAR algorithm, including stream function and velocity potential as control variables for the multivariate aspect, is described in detail. A few examples of analysis results are provided. The RUC 3dVAR in hybrid-isentropic-sigma coordinates is being implemented at the National Centers for Environmental Prediction (NCEP) in 2001.

Article / Publication Data
Active/Online
YES
ISSN
0177-7971
Volume
82
Available Metadata
DOI ↗
Fiscal Year
Publication Name
Meteorology and Atmospheric Physics
Published On
January 01, 2003
Publisher Name
Springer Verlag Wien
Print Volume
82
Print Number
1

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Not available

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Authors who have authored or contributed to this publication.